The long term objective of the proposed research is to identify and characterize those steps in viral RNA metabolism at which virus expression in cytomegalovirus (CMV) infected cells is regulated. The research plan is designed to investigate regulation at primary transcription and during post-transcriptional processing. In initial experiments to investigate temporal control of primary transcription total cell RNA extracted from cells at different times post-infection was analyzed by liquid DNA/RNA hybridization with RNA in excess. The complexity of viral-specific RNA present early was lower than that present late which suggests that primary transcription is regulated. Work in progress is directed toward identifying regions of the CMV genome which encode viral-specific RNAs transcribed at early and/or late times post-infection. Restriction enzyme fragments of CMV DNA-labeled in vitro will be hybridized in liquid with nuclear and cytoplasmic RNA extracted from cells at early and late times post-infection. An analysis of the data obtained should provide for the mapping of those regions of the CMV genome from which the RNA is transcribed. The size of viral-specific RNA will be examined by hybridization of in vitro labeled CMV DNA to blots RNA-sized by electrophoresis in methyl mercuric hydroxide agarose gels. An analysis of data obtained from such experiments should provide information basic to an understanding of post-transcriptional processing of CMV RNA transcripts. In addition, the transcription of DNA sequences found to differ between the Towne and AD169 strains of CMV is under investigation.